SPARC: fix PR ld/18841

SPARC: fix PR ld/18841

This fixes the last ld failures on SPARC64/Linux:

FAIL: Run pr18841 with libpr18841b.so
FAIL: Run pr18841 with libpr18841c.so
FAIL: Run pr18841 with libpr18841bn.so (-z now)
FAIL: Run pr18841 with libpr18841cn.so (-z now)

by mimicing what has been done on x86-64 and Aarch64 to fix the PR.

bfd/
	PR ld/18841
        * elf32-sparc.c (elf32_sparc_reloc_type_class): Return
        reloc_class_ifunc for ifunc symbols.
        * elf64-sparc.c (elf64_sparc_reloc_type_class): Likewise.